All suspended concrete decks in parking facilities contain reinforcing steel. When steel encounters both oxygen and water, rusting can occur. The process may be referred to as galvanic action, electrochemical corrosion, or ionic activity. If sodium chloride (de-icing salt) is used on roadways, it is carried into the garage on the underside of vehicles, drops to the deck surface, and eventually permeates through the concrete to the reinforcing steel (rebars), acting as an electrolyte in the presence of moisture and oxygen. This process greatly accelerates the rusting, which in turn reduces the steel to scale. This transformation of the steel increases its volume and produces extreme stress within the concrete slab, initially creating cracks and eventually spalled areas or potholes. The pressure created by corroding rebars can reach several thousand pounds per square inch.
Since no present system can eliminate oxygen from the concrete slab, it is customary to employ a waterproofing system using an impervious membrane and/or coating with a sealer, which stops the penetration of both moisture and chlorides into the slab. Another method of inhibiting corrosion is to apply a constant negative electric voltage to the reinforcing steel to reverse its anodic property.
An example of such a coating and voltage application presently in use is disclosed in U.S. Pat. No. 4,506,485 issued Mar. 26, 1985 to J. Apostolos which shows a coating of molten metal and a direct current circuit joining the coating and the embedded rebar. The Apostolos system suffers from the disadvantage that the coating provides a sacrificial anode and ablates over a period of time. Also the coating of Apostolos is relatively rigid and would be ineffective to bridge larger cracks often occurring in concrete.
The present invention provides a moisture impervious membrane or coating of improved conductivity which when given an electropositive charge reverses the anodic property of the reinforcing steel and thus all the reinforcing steel network becomes cathodic whereby no corrosion occurs.
Known waterproofing coating systems also suffer from the disadvantage that they are relatively inflexible and inelastic. Since hairline cracks in concrete can develop which are one-eighth of an inch or more in width, such coatings will fracture when stressed at the site of the crack. Shrinkage cracking of the coating may also occur.
The present invention provides a moisture impervious membrane or coating with inherent flexibility to bridge cracks without itself being fractured under normal extension under stress.